This invention relates to liquid crystal materials for use in electro-optic applications. More particularly, this invention relates to PDLC (polymer dispersed liquid crystal) materials.
Voltage imaging technology may be employed to detect and measure for defects in flat panel thin film transistor (TFT) arrays. According to this measurement technique, the performance of an array is simulated as if it were assembled into a TFT cell and then the characteristics of a TFT array are measured by indirectly measuring actual voltage distribution on the panel, or so-called voltage imaging, using an electro-optic (EO) light modulator-based detector.
A voltage imaging system in its most basic form includes an electro-optic (EO) modulator, an imaging objective lens, a charge coupled device (CCD) camera or other appropriate or similar sensor, and an image processor. The electro-optic sensor of the EO modulator is based on the light scattering characteristics of nematic liquid crystal droplets in a polymer matrix (polymer dispersed liquid crystal, or PDLC) film. In operation, the EO modulator is placed approximately 5-30 microns above the surface of a thin film transistor (TFT) array, and a voltage bias is applied across a transparent electrode of a layer of indium tin oxide (ITO) on a surface of the EO modulator. Thereupon, the EO modulator capacitively couples to the TFT array so that an electric field associated with the TFT array is sensed by the PDLC layer. Intensity of incident light transmitted through the PDLC layer is varied, i.e., is modulated, by any variations in the electric field strength across the liquid crystal (LC) material in the PDLC. This light is then reflected off a dielectric mirror and collected by the CCD camera or like sensor. A source of incident radiation, which may be for example infrared or visible light, is provided to illuminate the sandwich of TFT array, PDLC film and dielectric mirror.
The known method for EO modulator fabrication makes use of commercial NCAP (nematic curvilinear aligned phase) material, which is a form of PDLC that is suitable for making very large area light valves and displays. The NCAP device consists of micron size droplets of liquid crystal dispersed in and surrounded by a polymer film, such as in a sandwich between two layers of ITO Mylar film. Two patents, assigned to Photon Dynamics Inc., describe such processes: “Modulator Transfer Process and Assembly”, Michael A. Bryan, U.S. Pat. No. 6,151,153 (2000); and “Modulator Manufacturing Process and Device”, Michael A. Bryan, U.S. Pat. No. 6,211,991 B1 (2001). These patents are hereby incorporated by reference for all purposes.
While the above references are suitable for certain applications, there is a need in the art for improved electro-optic materials.